docs: def load_bmus(self, filename):
          """Load the best matching units from a file to the Somoclu object.
  
          :param filename: The name of the file.
          :type filename: str.
          """
          self.bmus = np.loadtxt(filename, comments='%', usecols=(1, 2))
          if self.n_vectors != 0 and len(self.bmus) != self.n_vectors:
              raise Exception("The number of best matching units does not match "
                              "the number of data instances")
          else:
              self.n_vectors = len(self.bmus)
          tmp = self.bmus[:, 0].copy()
          self.bmus[:, 0] = self.bmus[:, 1].copy()
          self.bmus[:, 1] = tmp
          if max(self.bmus[:, 0]) > self._n_columns - 1 or \
                  max(self.bmus[:, 1]) > self._n_rows - 1:
              raise Exception("The dimensions of the best matching units do not "
                              "match that of the map")